Applicator systems are used in a wide variety of manufacturing operations to apply compositions such as glue. For example, glue application systems are used in bottle labeling, can labeling, corrugated box making, manufacturing disposable diapers, and manufacturing other products that involve the application of glue.
Hot melt glue is one type of glue that is particularly well suited for applications where it is desired to apply glue at a high rate of speed. Applicants' assignee, B & H Manufacturing Company, Inc., provides labeling machines with a glue application system in which a glue wheel is provided with hot melt glue that is applied to a knurled roller and scraped off with a doctor blade in a process that is comparable to a gravure printing process.
While this system generally provides a reliable system for applying glue to labels at a high rate of speed, issues remain that relate to precise control of glue quantity, consistency of glue properties and minimizing the volume of glue required to secure a label. In addition, if the system is not properly set-up and maintained, glue splatter may result in application of glue to the vacuum drum that supports labels and the surrounding area. The removal of glue splatter may require periodic cleaning with solvents and may result in machine downtime. Re-circulation of large volumes of hot melt glue from the glue wheel type applicator results in repeatedly reheating a substantial quantity of the glue which may adversely affect glue properties. In addition, exposure of the glue to air on a glue wheel may result in degradation of the adhesive properties of the glue.
One alternative approach is disclosed in US2008/0014344A1 that suggests spraying a container with hot melt glue to adhere a leading end of a label from a cut and stack label magazine or a roll fed labeler to the container. Hot melt glue was proposed to be wiped onto the trailing edge of the label by a slit die nozzle that directly contacts the label to apply glue to the trailing edge that is then attached to the container or the label. A problem with this approach is that glue is extruded from the nozzle and “waits” on the head until the glue is smeared onto the trailing edge of the label material. A lack of control over the quantity of glue laid down on the label, or lay down weight, results in variation in the glue lay down weight as labeling speeds increase. This system fails to provide a method of controlling the lay down weight at variable speeds and is believed to have been limited to systems that apply labels at a rate of no more than about 300 containers per minute. When the slit die nozzle for hot melt glue application directly contacts the label, particularly with thinner labels, the label may be wrinkled or otherwise distorted. Another problem with this proposed approach is that the spring that is used to contact the slot gun with the trailing edge pad does not compensate for increases in centrifugal forces as labeling speeds increase which results in an increase in the contact force that may damage the trailing edge pad. Another problem is that may arise from variation in lay down weight is that the label may become jammed in the machine or otherwise misapplied to the container.
In other approaches, glue is provided to the slit die nozzle at a pressure that is controlled with the objective of maintaining a constant pressure level. However, as a valve is opened and closed to apply the glue an uneven distribution of glue is applied to the label. Another strategy for applying glue is to control the volume of glue applied by changing the speed of the glue pump in an effort to maintain a constant pressure. One problem with this approach is that it may result in an intermittent pattern of pressure spikes and thickness variation in the adhesive deposits. Another problem with this approach is that the quantity of glue applied is subject to variation.
Continuous application of an adhesive to a web of a plastic substrate in the manufacture of adhesive tape or pressure sensitive label material may be performed with a slit die coating nozzle that is controlled by controlling the volumetric flow of adhesive to a web that is continuous and moving at a constant rate of speed. However, volumetric control does not yield consistent and reliable application of glue with a controlled thickness when the speed of application changes. The glue is a compressible non-Newtonian liquid which renders volumetric control unreliable because it does not compensate for internal friction, the Reynolds number for the passages, changing viscosity and changes in shear strength caused by the speed of flow of the glue.
Others have proposed various solutions to improve upon the performance of the glue wheel approach. It should be understood that all alternative prior art approaches are not attempted to be described above. Applicants' development addresses the above issues and other issues relating to applying hot melt glue or otherwise extruding a non-Newtonian fluid onto a substrate through a nozzle. Applicants' development may be adapted to a wide variety of applications that are not limited to container labeling applications or the application of hot melt glue.
Some aspects of the developments are summarized below in greater detail.